Nicholas J. Payne

Spray dispersal from aerial silvicultural glyphosate applications

Abstract Spray dispersal was measured from overlaid crosswind swaths applied using an aerial silvicultural herbiciding method under various meteorological conditions. Spray applications were made with D8-46 hollow-cone nozzles mounted on a C188 fixed-wing aircraft flying at 45 m s−1, from which a simulant tank mix was applied at 30 l ha−1 and an equivalent glyphosate application rate of 1.8 kg ha−1. Spray lines were released at 10 m above ground over a short, open forest canopy in neutrally-stable and unstable atmospheric boundary layers with average wind speeds and air temperatures of 1.5–3.1 m s−1 and 15–20°C at release height. Peak deposits on ground plates and artificial foliage at 2 m above ground averaged 57 and 36% of the glyphosate application rate, occurring at downwind distances of 0 and 10 m, respectively. Deposits decreased by 90% between 0 and 50 m downwind, but showed a more gradual decrease between 50 and 200 m downwind to an average of 0.3 and 0.2% of the application rate for ground plates and artificial foliage, respectively. Up to sevenfold differences in deposit were observed at a given downwind distance under different meteorological conditions. The volume median diameters on ground cards and artificial foliage averaged 425 and 419 μm respectively at 0 m, and 103 and 79 μm at 200 m. Number median diameters on ground cards and artificial foliage averaged 252 and 197 μm respectively at 0 m, and 55 and 45 μm at 200 m.

Factors influencing aerial insecticide application to forests.

A successful aerial insecticide application is one that provides the desired degree of pest control at an economic cost, with little environmental impact. This paper discusses a broad range of factors that affect treatment efficacy and environmental impact from aerial insecticide application to forests. Efficacy is affected by parameters such as the choice of active ingredient and its application rate, the volume application rate, tank mix characteristics, the spray droplet size spectrum, and the timing of, and meteorological conditions during an application. Environmental impact is influenced by aspects such as active ingredient specificity, meteorological conditions during the application, avionics use and buffer zone width. Key differences between insecticide applications in forestry and agriculture are pointed out.

Developments in aerial pesticide application methods for forestry

Abstract Appropriate application methods play an important role in the success of pesticide use, both in relation to ensuring good efficacy and also minimising environmental impact. Scientific and technological developments pertaining to aerial pesticide application in forestry are reviewed, including developments in the design and characterization of hydraulic and rotary pesticide dispersal systems, application parameter research, use of spray dispersal modelling, and mitigation of pesticide environmental impact, including the use of buffer zones.

Spray deposits in a mature oak canopy from aerial applications of nuclear polyhedrosis virus and Bacillus thuringiensis to control gypsy moth, Lymantria dispar (L.)

Abstract Aerial spray applications were carried out to evaluate a naturally occurring nuclear polyhedrosis virus (NPV) for gypsy moth control. Mature oak forest plots were sprayed with a repeated application of 5 × 10 10 occlusion bodies (OB) ha −1 per application, and applications at 5 × 10 10 and 10 11 OB ha −1 , all with volume application rates of 5 l ha −1 per application. A Bacillus thuringiensis (Bt) treatment comprising a double application at 30 BIU in 2.4 l ha −1 was evaluated as a positive control. Spray applications were made with a fixed-wing aircraft equipped with rotary cage atomizers, in light winds with weak turbulence, moderate air temperatures and high relative humidity. Spray deposits in the treatment areas were assessed by microscopy and fluorometry, by means of a tracer dye. Deposit densities, drop-size spectra and volumetric deposits were quantified on oak leaves and artificial foliage in the tree canopy and on ground samplers. The NPV applications resulted in average deposit densities (number of stains cm −2 ) on oak leaves, artificial foliage and ground cards of 8, 15 and 11, respectively, and the Bt applications resulted in densities of 13, 10 and 12 on these substrates; coefficients of variation were high at 73–97%. Drop-size spectra on artificial foliage from the NPV applications had number and volume median diameters that averaged 81 and 279 μm. By contrast the foliar drop-size spectra for Bt applications had number and volume median diameters that averaged 31 and 95 μm, due to lower flow rates and faster cage rotation. Volumetric spray deposits on artificial foliage from the NPV applications averaged 11% of the volume application rate compared to 25% on the ground. The Bt applications resulted in average volumetric foliar and ground deposits of 17 and 21% of the application rate. Comparisons with published data are made, and a suggestion for improving NPV applications for gypsy moth control with the use of finer sprays and more turbulent conditions.

Airborne permethrin and off-target deposits from an aerial ultra-low volume silvicultural spray

A 16 ha forested site with canopy height averaging 7 m was aerially sprayed with an aqueous permethrin emulsion, using active ingredient and volume application rates of 70 g ha−1 and 41ha−1 respectively. A fixed-wing aircraft equipped with Micronair AU 3000 atomizers dispersed a spray with a volume median diameter of 65 μm in a stable atmospheric boundary layer with a wind speed of 2.3 m s−1 and air temperature of 19°C at the spray height of 18 m above ground level. Measurements were made of airborne permethrin and off-target spray deposits on spruce foliage and fine-toothed combs at 2 m above ground level, and glass plates and Kromekote cards placed horizontally on the ground at various distances up to 250 m from the treatment area. Airborne permethrin was reduced by 60% between 0 and 250 m; over this distance the drop numbers per spruce needle decreased from 17 to 2.6 and drop densities on Kromekote ground cards and combs from 22 to 5.6 and from 87 to 18 drops cm−2. Volume median diameters on the Kromekote cards and combs were 49 and 38 μm, and showed no significant change between 0 and 250 m. Permethrin deposits on glass plates and aluminium combs decreased from 23 to 6 ng cm−2 and from 52 to 10 ng cm−2 between 0 and 250 m. Deposits on glass plates were compared with values calculated using a published swath superposition model and found to be in good agreement.

Development and evaluation of a method for the design of spray applications: aerial tebufenozide applications to control the eastern spruce budworm, Choristoneura fumiferana (Clem.)

Abstract A novel approach to the design of insecticide spray applications was developed and evaluated in field trials to assess the efficacy of the insect moulting hormone analog tebufenozide (Mimic ® ) against the eastern spruce budworm, Choristoneura fumiferana (Clem.). The pest biology, and habitat and pesticide characteristics were used as a basis to derive the required active ingredient (a.i.) and deposit density. Ingestion is the primary exposure route; an LD 95 acquisition through foliage consumption by fourthinstar larvae was used to establish a target dose of 15 ng a.i. cm −2 in one drop per needle (2.5 cm −2 ). A range of a.i. and volume application rates were selected based on the required densities, canopy leaf area index and projected spray losses to the understorey and by drift; application rates of 35, 70 and 140 g a.i. 1 ha −1 were employed, with volume application rates of 1, 2 and 4 L ha −1 . Coniferous forest plots were aerially treated, resulting in average deposit densities (droplets cm −2 ) on artificial foliage between 0.8 and 3.7, with averge volumetric deposits between 7 and 30% of volume application rates. Population control was satisfactory, except for those applications at 35 g a.i. in 2 L and 70 g in 4 L ha −1 for which low deposit densities were observed. This approach to spray application design was found to be of scientific value and is adaptable to other insecticide applications.

Spray deposits from aerial insecticide spray simulant applications to a coniferous plantation in low and high wind speeds

Abstract Aerial insecticide applications were made on a jack pine plantation in low and high wind speeds, using a fixed-wing aircraft equipped with rotary atomizers. A 16 ha area with an average canopy height of 6.5 m was sprayed with a suspension of fluorescent particles in tripropylene glycol monomethyl ether at 0.42 l ha−1, using a 65 m swath width. The spray was released from 18 m above ground and had a volume median diameter of 41 μm. Wind speeds at release height were 1.2 and 4.5 m s−1 in trials 1 and 2, and the air layers between canopy top and spray release height were stable and unstable respectively. Average drop counts per conifer needle from trials 1 and 2 were significantly different at 0.91 and 1.92, and foliar deposits at 4 and 6 m were significantly greater in the high wind trial. Drop counts per needle increased with height and the count ratios at 2, 4, and 6 m were 1:2:4 and 1:3:10 in trials 1 and 2. Drop count distributions on needles from different heights showed significant differences and a larger proportion of needles received drops in the high wind trial, implying the potential for improved insecticide efficacy. Drop densities (cm−2) on Kromekote ground cards from trials 1 and 2 were significantly different at 3.26 and 1.85, implying substantially reduced contamination of the understorey in high winds. Drop sizes were similar, with average volume and number median diameters of 71 and 45 μm. Drop sizes on Kromekote combs placed in the canopy were also similar in both trials, with average volume and number median diameters of 49 and 21 μm. The results indicate an excellent opportunity for improving on-target spray deposits and efficacy while reducing understorey contamination from silvicultural insecticide applications, as well as their cost and temporal constraints.